There are raised many concerns that the use of fossil energy is increasing the earth greenhouse effect to an extent that may turn dangerous. Thus the present consumption of fossil fuels should preferably be replaced by energy sources/carriers that are renewable and sustainable for our climate and environment.
One such energy source is solar light, which irradiates the earth with vastly more energy than the present and any foreseeable increase in human energy consumption. However, solar cell electricity has up to date been too expensive to be competitive with nuclear power, thermal power, hydroelectric power etc. This needs to change if the vast potential of the solar cell electricity is to be realised.
The cost of electricity from a solar panel is a function of the energy conversion efficiency and the production costs of the solar panel. Thus the search for cheaper solar electricity should be focused at high-efficient solar cells made by cost-effective manufacturing methods.
The presently dominating processing route of silicon based solar panels may roughly be described as follows; manufacturing the solar grade feedstock in the form of crystalline blocks of high purity silicon, sawing the blocks into a set of thin wafers, cell processing each wafer to a solar cell, and then mounting the solar cells to form solar panels which are further installed and integrated as solar systems.
The present dominating processing route is however encumbered with a very low utility degree of the silicon feedstock, mainly due to two factors; the present day sawing process requires a minimum thickness of the wafers of 150-200 μm while the most significant photovoltaic active layer in the wafer is only about 20-30 μm, and the formation of the wafers by sawing results in about half of the solar grade silicon feed material being lost as kerf. It is thus highly desirable to find a process route for silicon based solar panels without need for sawing the wafers and which may form wafers with a thickness in accordance with the photovoltaic requirements.
Further, to create a solar module, cells are typically connected in a series electrical circuit such that the positive electrical output of the module is connected to the anode regions of the first cell and the negative electrical output of the module is connected to the cathode regions of the last cell in the series. For cell with an n-type base region, the n-type base region is the cathode and the p-type emitter regions form the anode. For cell with a p-type base region, the p-type base region is the anode and the n-type emitter regions form the cathode. The cells in between are connected such that the emitter regions of the first cell are connected to the base regions of the second cell, the emitter regions of the second cell are connected to the base regions of the third cell and so on until all cells are connected in a string. The interconnect method describes how this series electrical connection of cells can be achieved. Alternate circuit topologies are also possible using this interconnect method, such as cells connected as a parallel circuit or as a combination of series and parallel circuits, although these are generally not preferred since higher total currents are produced which require larger conductor cross-sections.
The cell metallization is a patterned layer or layers of metal disposed onto each solar cell such that electrical current can flow from the emitter and base semiconductor regions of the solar cell into the emitter and base metallization regions. The emitter and base metallization regions are patterned such that the emitter metal and the base metal do not make a direct electrical connection to each other. In general, a reduced metal-semiconductor contact area is preferred to reduce carrier recombination at the contacts, while a larger finger conductor area is preferred for lower resistive losses.